Amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole

ABSTRACT

Amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole with at least one fluoro comonomer selected from one or more of ten defined classes having a recited minimum mole proportion of perfluoro-2,2-dimethyl-1,3-dioxole, in no event less than 65%, have high glass transition temperatures of 140° C. or higher, low indices of refraction, and good physical properties, and low dielectric constants, which make them suitable for cladding optical fibers as well as for many electronics applications, including the manufacture of substrates for circuit boards. They all are soluble at room temperature in perfluoro(2-butyltetrahydrofuran), which makes it practical to apply them as coatings from solution.

CROSS-REFERENCE TO RELATED

This is a division of my copending application Ser. No. 07/361,412,filed June 5, 1989, now U.S. Pat. No. 4,935,477 which was acontinuation-in-part of application Ser. No. 07/148,579 filed Jan. 26,1988, and now abandoned, which was a division of application Ser. No.06/904,095 filed Sept. 4, 1986, now U.S. Pat. No. 4,754,009, which was acontinuation-in-part of application Ser. No. 06/723,649 filed Apr. 16,1985 and now abandoned, which was a division of application Ser. No.06/591,486 filed Mar. 20, 1984, now U.S. Pat. No. 4,530569, which was acontinuation of application Ser. No. 06/294,789 filed Aug. 21, 1981 andnow abandoned.

BACKGROUND OF THE INVENTION

This invention relates to certain amorphous fluoropolymers which areparticularly suitable as cladding materials in optical fiberconstructions as well as in certain electronics applications, moldedarticles, and films.

While tetrafluoroethylene homopolymers and copolymers have manyexcellent properties, they usually suffer from low modulus, especiallyat elevated temperature; poor creep resistance; insolubility; and insome cases intractability. Various fluoropolymers have been proposedfrom time to time for cladding optical fibers, mainly because of theirlow refractive indices. A good polymeric cladding material for opticalfibers should be completely amorphous because crystallites present inpolymers would cause light scattering. Further, it should have a highglass transition temperature, Tg, especially if intended for use at hightemperatures because above its Tg it would lose some of its desirablephysical properties and in particular it would be unable to maintaingood bonding to the fiber core. A desirable Tg would be above 140° C.,preferably above 180° C., especially above 220° C. Suitable, entirelyamorphous fluoropolymers having significantly high Tg's have not beenheretofore reported.

U.S. Pat. No. 3,978,030 to Resnick describes certain polymers ofperfluoro-2,2-dimethyl-1,3-dioxole (PDD), which has the followingformula: ##STR1## The above patent describes both homopolymers of PDD,which are not further characterized, and a crystalline copolymer withtetrafluoroethylene (TFE), which has a melting point of about 265° C.

Since Resnick's discovery of PDD homopolymer, it has been establishedthat the material is amorphous and has a very high Tg of about 330° C.The homopolymer, however, is not readily melt-processible because ofpoor flow and some degradation.

Crystalline copolymers of PDD with TFE cannot be used in manyapplications, where, for example, optical clarity, dimensionalstability, solubility, or high Tg is required.

The polymers of U.S. Pat. No. 3,978,030 have thus not been producedcommercially, in spite of the fact that perfluoro polymers havingdesirable properties would have many possible uses in various hightechnology applications.

It has now been found that the dioxole PDD forms amorphous copolymersthat have unique properties that make them particularly suitable for anumber of special applications requiring high performance.

SUMMARY OF THE INVENTION

According to this invention, there are now provided amorphous copolymersof 58-99 mole % of perfluoro-2,2-dimethyl-1,3-dioxole with complementaryamounts of more than one comonomer selected from the class consisting ofthe following compounds:

(a) tetrafluoroethylene,

(b) chlorotrifluoroethylene,

(c) vinylidene fluoride,

(d) hexafluoropropylene,

(e) trifluoroethylene,

(f) perfluoro(alkyl vinyl ethers) of the formula CF₂ ═CFOR_(F), whereR_(F) is a normal perfluoroalkyl radical having 1-3 carbon atoms,

(g) fluorovinyl ethers of the formula CF₂ ═CFOQZ, where Q is aperfluorinated alkylene radical containing 0-4 ether oxygen atoms,wherein the sum of the C and O atoms in Q is 2 to 10; and Z is a groupselected from the class consisting of --COOR, --SO₂ F, --CN, --COF, and--OCH₃, where R is a C₁ -C₄ alkyl,

(h) vinyl fluoride, and

(i) (perfluoroalkyl)ethylene, R_(f) CH═CH₂, where R_(f) is C₁ -C₈ normalperfluoroalkyl radical;

the glass transition temperature of the copolymers being at least 140°C.;

the maximum mole percentage, M_(a) . . . M_(i), of each comonomer in thecopolymers being as follows:

(a) for tetrafluoroethylene, M_(a) =35,

(b) for chlorotrifluoroethylene, M_(b) =42,

(c) for vinylidene fluoride, M_(c) =20,

(d) for hexafluoropropylene, M_(d) =15

(e) for trifluoroethylene, M_(e) =30

(f) for CF₂ =CFOR_(F), M_(f) =30,

(g) for CF₂ =CFOQZ, M_(g) =20,

(h) for vinyl fluoride, M_(h) =25, and

(i) for R_(f) CH═CH₂, M_(i) =10;

and the amount of each comonomer other than PDD being such that the sum,S, of the ratios of their mole percentages, m_(a) . . . m_(i), to themaximum percentage of all such comonomers, 42 mole %, is no larger than1, as shown below:

    S=m.sub.a /42+m.sub.b /42+ . . . +m.sub.i /42≦1.

There also are provided dipolymers of 58-99 mole % ofperfluoro-2,2-dimethyl-1,3-dioxole with a complementary amount of anyone of the above comonomers other than tetrafluoroethylene, the maximummole percentage, M_(b) . . . M_(i), of each comonomer being as shownabove, and the glass transition temperature of those dipolymers being atleast 140° C.

As used herein, the term "complementary" means that the mole percentageof perfluoro-2,2-dimethyl-1,3-dioxole plus the mole percentages of allthe above comonomers (a) through (i), present in the copolymer addtogether to 100%.

DETAILED DESCRIPTION OF THE INVENTION

The copolymers of the present invention preferably have a T_(g) of atleast 180° C. When such copolymers contain more than one comonomercopolymerized with PDD, the value of S is less than 1. The especiallypreferred copolymers of the present invention have a T_(g) of at least220° C. When those copolymers contain more than one comonomercopolymerized with PDD, the value of S is significantly less than 1, forexample, 0.8 or less.

All the principal monomers used in this invention are known to the art.The perfluoro (alkyl vinyl ethers) (f) include perfluoro(methyl vinylether), perfluoro(ethyl vinyl ether), and perfluoro(npropyl vinylether). The ethers (g) include, i.a., methylperfluoro(3,6-dioxa-4-methyl-8-nonenoate) (further referred to as EVE)represented by the following formula ##STR2## andperfluoro(4-methyl-3,6-dioxa-7-octenyl) sulfonyl fluoride (furtherreferred to as PSEPVE) represented by the following formula ##STR3## TFEis made in large quantities by E. I. du Pont de Nemours and Company;other suitable representative monomers are available from the followingsources: VF₂, chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP),vinyl fluoride, and trifluoroethylene from SCM Specialty Chemicals,Gainesville, Fla.; perfluoro(methyl vinyl ether) (PMVE),andperfluoro(propyl vinyl ether) (PPVE) are made as described in U.S. Pat.No. 3,180,895; (EVE) is made as described in U.S. Pat. No. 4,138,740;and PSEPVE is made as described in U.S. Pat. No. 3,282,875. PDD isdescribed in the above-mentioned U.S. Pat. No. 3,978,030.

It has now been discovered that PDD can be copolymerized with any one ormore of the above-named monomers to amorphous copolymers.

The amorphous copolymers of the present invention, are soluble at roomtemperature in perfluoro (2-butyltetrahydrofuran), which is a commercialsolvent available from 3M Company under the tradename FC-75. Inaddition, they have the following outstanding combination of properties:

1. high glass transition temperatures;

2. high moduli, especially at elevated temperatures;

3 high strengths, especially at elevated temperatures;

4. low creep under compressive load.

5. melt fabricability at moderate temperatures;

6. fabricability into films and coatings by solvent casting;

8. unusually low refractive indices;

9. excellent dielectric properties;

10. excellent chemical resistance.

The first four characteristic properties of the copolymers of thepresent invention are particularly advantageous in applications wherethe polymer must bear a load at an elevated temperature. Because oftheir chemical inertness and excellent dielectric properties, they alsoare suitable for a number of specialized electrical applications. Also,because of their chemical inertness, good optical properties, and goodphysical properties, they are suitable for the manufacture of opticallenses. The polymers of this invention can also be filled or reinforcedwith solid substances to make composite materials. The additivesinclude, i.a., graphite, graphite fibers, aramid fibers, mica,wollastonite, glass fibers, etc. Fibrous material may be in the form ofloose fibers, fabrics, or mats. Such composite materials showenhancement of desirable properties such as modulus, for example.

Films of the amorphous copolymers of this invention are useful whenthermally laminated to other polymeric films or metal foils. A laminateof the amorphous copolymers of this invention with copper foil is asuperior substrate for flexible circuit production because the copolymerbonds directly with the copper without the necessity for an interveningadhesive. Conventional copper/adhesive/polyimide/adhesive/copperstructures for electronic circuit substrates have the deficiency of highdielectric constant material next to copper. This limits the ultimatespeed of the electronic circuit. A laminate of copper/amorphouscopolymer/copper permits very high circuit speeds because the amorphouscopolymer film has a low dielectric constant (2.1) and can be thermallybonded directly to circuit copper.

A thermal laminate of amorphous copolymer/polyimide/amorphous copolymeris useful as an electronic circuit substrate. Compared to polyimide filmitself, this laminate is a superior circuit substrate because (a) it maybe thermally bonded to copper foil without adhesive; (b) the low waterabsorption of the amorphous copolymer gives the substrate greaterdimensional stability in humid environments; and (c) the low dielectricconstant of the amorphous copolymer allows the fabrication of a highspeed circuit.

A thermal laminate of amorphous copolymer/polyimide is useful as avacuum bag for the curing of parts such as helicopter blades made fromcarbon fiber reinforced thermoset. The high glass transitiontemperature, thermal stability and low surface energy of the amorphouscopolymer give the laminate excellent release properties when this sideis placed against the thermoset part to be cured. The polyimide layer ofthe laminate provides strength to prevent pinholing when the bagenclosing the thermoset part is evacuated and raised to curingtemperature. After curing and cooling the laminate is easily separatedfrom the part.

A thermal laminate containing film of amorphous copolymer as its outerfaces and a film of oriented polypropylene as the core is useful as alow-cost film structure with outstanding chemical resistance and stainresistance combined with excellent mechanical properties. Such laminatescan be used to protect sensitive instruments from environmental damage.

Pipe, tubing and fittings which are made from or lined with theamorphous copolymer of this invention prevent the contamination of theprocess liquid with metal ions, plasticizer, or degradation productsfrom the fluid handling system. Such fluid handling components are ofvery high purity, are inert to most common chemicals, and are easilyfabricated by injection molding, extrusion, machining from stock.Alternatively, fluid handling system components may be fabricated frommetal, glass, or other plastic and subsequently lined with amorphouscopolymer of this invention by solution coating, dispersion coating, orelectrostatic powder coating. In addition to pipe, tubing and fittings,other useful fluid handling articles made from the amorphous copolymersof this invention are pump housings, pump impellers, valve bodies, valvestems, valve seals, diaphragms, tanks, trays, pipettes, laboratoryvessels. Such articles are especially useful in semiconductor processingfluid handling systems where parts-per-billion purity is required inprocess water and chemicals. Also, in molecular biology researchlaboratories where extreme purity is required, and microgram quantitiesmust be completely released from the vessels in which they are handled,the fluid handling articles made from the amorphous copolymer of thisinvention are particularly useful.

The amorphous copolymers of this invention are particularly useful whenfabricated into articles to transport materials and components throughchemical treatment processes. For example in the manufacturing processfor semiconductor chips the silicon wafers must be transported through aseries of chemical treatment steps; the containers in which the siliconwafers are carried must be chemically inert to prevent contamination ofthe chips, and they must be rigid and dimensionally stable to permitprecise automatic positioning at each stage of the process. Compared tothe conventional fluoroplastics used for such wafer carriers, e.g., thecopolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether), theamorphous copolymers of the present invention have greater rigidity andgreater dimensional stability. This advantage makes possible thefabrication of larger wafer carriers, e.g, baskets to hold siliconwafers of 30 cm in diameter; wafer carriers made from conventionalfluoroplastics are too low in flexural modulus to be useful for waferslarger than about 15 cm in diameter.

Other conveying system components for which articles made from theamorphous copolymers of the present invention are especially well suitedare guide rails, conveyor belt links, bearings and rollers, clamps,racks, hooks, positioning pins, robot arm jaws and fingers, gears, camsand similar mechanical parts which must be precisely engineered, havegood high temperature mechanical properties, retain dimensions, bechemically pure and chemically inert. Conveying system components madefrom the amorphous copolymers of this invention exposed to corrosivechemicals or ultrapure water are superior to all conventionalfluoroplastics because of the superior high temperature mechanicalproperties and dimensional stability of the polymers of this invention.

The low dielectric constant (2.1) and low coefficient of thermalexpansion of the amorphous copolymers of this invention make themespecially useful as dielectrics in electrical and electronicapplications. For example, the dielectric used between the separatecircuit layers in high speed digital multi-layer circuit boards must bevery low in dielectric constant and be very dimensionally stable from-20° C. up to soldering temperature of approximately 225° C. Polyimideis dimensionally stable but has a high dielectric constant (>3); inaddition it is susceptible to atmospheric moisture; the amorphouscopolymers of this invention do not have these deficiencies, andmulti-layered circuits which have this polymer as a dielectric betweencircuit layers are capable of greater speed and greater circuit density.

The low moisture absorption, outstanding chemical resistance, purity,thermal stability, and dimensional stability of the amorphous copolymersof this invention make them especially suited for the protection ofsensitive electronic circuits and components. Unlike conventionalfluoroplastics the polymers of the present invention can be dissolved toform coating and encapsulating solutions. For example, a so-called"smart connector" may be encapsulated by dipping it, pins up, in asolution of the amorphous copolymer of Example 1 and evaporating theFC-75 solvent to leave a protective film of polymer to excludeenvironmental water and corrosive chemicals. In another embodiment thepolymers of this invention may be used instead of a thin layer of gold,so-called "gold flash", to protect electronic connectors from corrosionfrom atmospheric chemicals. Whole electronic or electro-optic circuitsmay be encapsulated by the amorphous copolymers of this invention by asolution coating process, which is not possible with conventionalfluoropolymers because of their insolubility in practical solvents. Itis well known that aqueous dispersions of conventional fluoropolymersmay be used to impregnate and encapsulate articles such as glass fabricand metal parts; however, the application of such dispersions is limitedto substrates which can tolerate the high baking temperatures (>200° C.)required to fuse the fluoroplastic into a pinhole-free coating. Incontrast to aqueous dispersions of conventional fluoroplastics,solutions of the amorphous copolymers of the present invention may beapplied to temperature sensitive substrates such as electronic circuitsor electronic components made from thermoplastics, and the solventevaporated at moderate temperature (100° C. or less) to leave aprotective polymer film without the necessity of high temperature bakingto fuse the polymer.

As the amount of PDD in the copolymers of the present inventionincreases, the Tg also increases, although not necessarily in a linearfashion.

Tg is determined by differential scanning calorimetry (DSC) according toASTM method D-3418. Examination of the DSC curve shows only a secondorder transition and no first order transition, indicating the absenceof crystallinity. The relative proportions of the comonomers in thecopolymer can be determined by fluorine-19 nuclear magnetic resonancespectroscopy (¹⁹ F NMR). The proportion of hydrogen-containing monomerscan be determined by proton NMR together with ¹⁹ F NMR.

The proportions of comonomers in some copolymers also can be determinedby x-ray fluorescence (XRF), e.g. using a Philips Electronic Instruments1404 XRF spectrometer. Calibration of x-ray fluoroescence intensity as afunction of weight % oxygen and fluorine can be accomplished using threepolymer samples of known composition which bracket the anticipatedfluorine and oxygen content of the unknown PDD copolymers.

The copolymers of PDD with the fluoromonomers of this invention arereadily melt-processible, so that they can be fabricated into articlesby such techniques as, e.g., injection molding and extrusion.Furthermore, they have low refractive indices, which is a particularlydesirable feature for optical fiber cladding. Since they are soluble inFC-75, they can be conveniently applied to substrates, such as opticalfibers or flexible or rigid circuit boards, from solution to give thinpolymer layers. Furthermore, films of these copolymers are clear andtransparent, compared with hazy or translucent films of crystallinepolymers. For this reason, the amorphous copolymers of the presentinvention are suitable for such applications as, for example, windowsfor chemical reactors, especially for processes using or manufacturinghydrogen fluoride.

It is to be noted that, while PDD homopolymers also are amorphous andhave good chemical properties, they are not readily melt-fabricablebecause of some degradation occurring at the high processingtemperatures required.

Copolymerization is carried out in the presence of a free radicalgenerator at a temperature suitable for the initiator chosen. Wellagitated pressure equipment and a nontelogenic solvent or diluent shouldbe used, preferably one that has sufficient volatility to permit easyremoval from the polymer.

This invention is now illustrated by the following examples of certainpreferred embodiments thereof, where all parts, proportions, andpercentages are by weight, unless otherwise indicated. Most Tg's weredetermined using Du Pont Differential Thermal Analyzer Model 1090 with910 or 912 DSC modules. All units have been converted to SI units.

COMPARATIVE EXAMPLE A

A mixture of 5.0 g of PDD, 0.100 g of4,4'-bis(t-butylcyclohexyl)peroxydicarbonate, and 40.0 g of1,1,2-trichloro-1,2,2-trifluoroethane was placed in a pressure tube. Themixture was thoroughly degassed, sealed, and placed in a constanttemperature bath at 30° C. for 20 hours. The polymerization mixtureappeared as a thick, translucent slurry of polymer particles dispersedin 1,1,2-trichloro-1,2,2-trifluoroethane. The volatile material wasremoved by distillation, and the polymer residue was dried at 150° C.for 20 hours to give 4.7 g of PDD homopolymer. The products of fouridentical runs were combined. The polymer had two glass transitiontemperatures, at 333° and 350° C. The PDD homopolymer could not bemelt-fabricated by compression molding without some degradation(evidenced by gas evolution). Moldings could be obtained within thetemperature range 355°-370° C. Above 370° C., the degradation was quitenoticeable; below 350° C., the polymer flow was insufficient forproducing moldings, and coalescence to a homogeneous test slab was notachieved.

PDD homopolymer could be cast from perfluoro(2-butyltetrahydrofuran)solution. That material had good physical properties (e.g., highmodulus) but this technique is impractical for thick parts.

EXAMPLE 1

A 2-liter vertical reactor equipped with a four-bladed impeller typeagitator was charged with 1500 ml of deoxygenated, deionized water, 3.75g of ammonium perfluorononanoate surfactant, and 4.70 g of ammoniumsulfite. The reactor was pressurized with chlorotrifluoroethylene(CTFE), then vented.

With the agitator running at 600 rpm, 25 ml of a 7% ammonium persulfate(APS) solution in water was introduced into the reactor heated to 60°C.; next, an initial charge of 2.63 g of CTFE and 16 g of PDD was added.After the mixture had been stirred for 30 minutes, continuous feed of5.25 g/hr of CTFE, 32 g/hr of PDD (CTFE/PDD mole ratio of 0.344) and 10ml/hr of APS solution was begun and continued for 4.5 hours. The reactorwas cooled to 30° C., and a dispersion containing 9.4% of solids wasrecovered.

Concentrated nitric acid (15 ml) was added to the dispersion in ablender and agitated. The dispersion separated into a water phase and acopolymer phase. The copolymer was filtered off, dried in an oven at110° C. for 24 hours, and further dried in a vacuum oven at 100° C. toremove any traces of water. The copolymer was next fluorinated for 6hours at 100° C. with a 25:75 fluorine/nitrogen mixture in a reactorwhich had been evacuated and purged with nitrogen. The total gas flowamounted to 0.132 part of fluorine per part of copolymer. The reactorwas then purged with nitrogen and cooled. The granulated amorphouscopolymer, which was recovered, had a single glass transitiontemperature of 174° C. Its composition was 19.7 mole % CTFE and 80.3mole % PDD.

EXAMPLE 2

A copolymer of PDD and CTFE was prepared in the same manner as describedin Example 1, except that the initial charge consisted of 2.66 g of CTFEand 16 g of PDD (CTFE/PDD mole ratio of 0.348). The dispersion recoveredfrom the polymerization reactor contained 9.03% solids. The resultingcopolymer was fluorinated as described in Example 1. It was amorphous,with a single Tg of 184° C. and had a monomer composition of CTFE/PDD of23:77 mole %.

EXAMPLE 3

A cold 200 ml Hastelloy (TM) C shaker tube was charged with 30 g of1,1,2-trichloro-1,2,2-trifluoroethane, 6 g (0.0246 mole) of PDD, 0.02 gof 4,4'-bis(t-butylcyclohexyl)peroxydicarbonate, and 1 g (0.00237 mole)of EVE. The tube was evacuated while cold and flushed several times withnitrogen, then agitated 12 hours at 40° C. The resulting dipolymer wascollected and dried 24 hours at 100° C. in a vacuum oven at 20.3 kPapressure. The yield of dipolymer was 4.5 g (64% conversion). Thedipolymer was amorphous, had a Tg of 186.7° C., and contained 90.8 mole% of PDD, as determined by ¹⁹ F NMR spectroscopy. Its inherent viscositywas 0.0735 m³ /kg, as measured at 27° C. in a 3.33 kg/m³ solution inFC-75®.

EXAMPLE 4

A cold 240 ml Hasteloy (TM) C shaker tube was charged with 50 g of1,1,2-trichloro-1,2,2-trifluoroethane and 10 g (0.041 mole) of PDD, 0.1g of 4,4'-bis(t-butylcyclohexyl)peroxydicarbonate. The tube wasevacuated cold and was charged with 2 g (0.0133 mole) ofhexafluoropropene. The tube was agitated at 60° C. for 2 hours and at70° C. for 2 hours. The resulting dipolymer was collected and dried at130° C. in a vacuum oven for 10 hours. A white dipolymer powder, 7.4 g(62% conversion) was obtained. The dipolymer was amorphous, had a Tg of265°-270° C., and contained 94.6 mole % PDD. The inherent viscosity ofthe dipolymer was 0.0293 m³ /kg, as measured at 23° C. in a 3.33 kg/m³solution in FC-75®.

EXAMPLE 5

A 500 ml creased, jacketed flask equipped with a mechanical stirrer,nitrogen sparger, and syringe inlet was charged with 200 ml of water and1.02 g of ammonium perfluorononanoate. The flask was warmed up todissolve ammonium perfluorononanoate and then cooled to roomtemperature. Concentrated ammonium hydroxide (3 ml), sodium sulfite(0.85 g, 0.0067 mole), PDD (25 g, 0.1025 mole), and perfluoro(n-propylvinyl ether) (11.7 g, 0.044 mole) were charged into the flask in thatorder. The contents of the flask were stirred at 500 rpm. Potassiumpersulfate (0.90 g, 0.0033 mole) was injected into the flask. Thereaction mixture was stirred overnight (total reaction time 21.5 hours).The resulting coagulum was filtered off, and the remaining latex wasdiluted with methanol, then coagulated with 20 g of magnesium sulfate in100 ml of water. The resulting dipolymer was collected, washed threetimes with a methanol/water mixture, and dried overnight. The drydipolymer weighed 12.6 g. The inherent viscosity of this amorphouscopolymer was 0.0904 m³ /kg, as measured at 30° C. in a 3.33 kg/m³solution in FC-75®, and its Tg was 228° C. The approximate mole fractionof PDD in this dipolymer is 92%.

EXAMPLE 6

A cold 240 ml Hastelloy (TM) C shaker tube was charged with 80 g of1,1,2-trichloro-1,2,2-trifluoroethane, 15 g (0.0615 mole) of PDD, 2 g(0.00474 mole) of EVE and 0.05g of 4,4'-bis(t-butylcyclohexyl)peroxydicarbonate. The tube was sealed, evacuated while cold, and wascharged with 0.8 g (±0.2 g) (0.008 mole) of TFE. The tube was agitatedat 40° C. for 12 hours. The resulting terpolymer was collected and dried20 hours in a vacuum oven at 120° C. A white resin 10.5 g (59%conversion) was obtained. This terpolymer was amorphous and had a T_(g)of 162° C. The inherent viscosity of the terpolymer was 0.0734 m³ /kg,as measured at 25° C. in a 3.33 kg/m³ solution in FC-75®. The terpolymerhad a composition of PDD/TFE/EVE=79.5/16.5/4.0 (mole %) as determined byF-19 NMR spectroscopy.

EXAMPLE 7

A 2-liter horizontal reactor equipped with a paddle stirrer was chargedwith 1150 ml of deionized water, 4 g of ammonium perfluorononanoate, and1.25 g of ammonium sulfite.

With the stirrer turning at 70 rpm, an initial charge of 14 g ofperfluoro(methyl vinyl ether) (PMVE) and 32 g of PDD (PMVE/PDD moleratio of 0.643) was introduced into the reactor heated to 65° C. Then,30 ml of a 1% ammonium persulfate solution (APS) in water was added. Themixture was stirred at 65° C. for 10 minutes, after which a continuousfeed of 20 g/hr of PMVE, 48 g/hr of PDD, and 30 ml of the APS solutionwas begun and continued for 6 hours. The reactor was cooled to 30° C. Adispersion containing 11.5% of solids was recovered.

The dispersion was coagulated by addition of 10 ml of concentratednitric acid in a blender, separating into a water phase and a copolymerphase. The copolymer was dried 24 hours at 105° C. in an oven at normalpressure and then at 100° C. in a vacuum oven to remove any traces ofwater. The copolymer was then fluorinated at 100° C. for 6 hours in apreviously evacuated and nitrogen-purged reactor with a 25:75fluorine/nitrogen mixture, which was passed at the total rate of 0.085part of fluorine per part of copolymer. The resulting amorphouscopolymer had a single Tg of 173° C. and had a monomer composition ofPMVE/PDD of 13:87 mole %.

EXAMPLE 8

A 2 liter horizontal polymerization kettle equipped with a paddle typeagitator was charged with a solution of 1100 g of demineralized watercontaining 2.0 g of ammonium sulfite and heated to 60° C. Thepolymerization kettle was evacuated to 68 kPa. To the evacuatedpolymerization kettle were added 50 ml of1,1,2-trichloro-1,2,2-trifluoroethane and 8.0 g of Asahi Glass "Surfion"S111S fluorosurfactant (which is essentially ammoniumperfluorononanoate). With the agitator still off, 26.7 ml (42.7 g, 0.175mole) of PDD was pressured into the polymerization kettle to give apressure of 90 kPa. Then 13.5 g (0.116 mole) of CTFE was added, raisingthe pressure to 207 kPa. The mole fraction of CTFE in the monomer chargethus was 39.9%. After both monomers were added, agitation was begun at arate of 200 rpm and a 1% aqueous solution of ammonium persulfateinitiator was added at a rate of 150 ml/hr. After 36 minutes of feedingthe initiator at this rate, reactor pressure had dropped to 179 kPa,indicating that polymerization had begun. At this point, ammoniumpersulfate addition was reduced to a feed rate of 60 ml/hr. PDD was nowfed at a continuous rate of 51.7 ml/hr (82.7 g/hr, 0.34 mole/hr), andCTFE monomer was fed at a continuous rate of 26.7 g/hr (0.23 mole/hr)until a total of 155 ml (248 g, 1.02 mole) of PDD and 80.1 g (0.69 mole)of CTFE had been added after the initial pressure drop. The molefraction of CTFE in the continuously fed monomer thus was 40.4%.Addition of both monomers and initiator was stopped at this time. Aftera further pressure drop to 158 kPa, the polymerization kettle was ventedand the contents were recovered.

The resulting cooled latex weighed 1,732 g and had a solids content of19.8%. An additional 554 ml of deionized water was added to dilute thelatex to 15% solids. The diluted latex was transferred to a 5 L jacketedflask equipped with a mechanical paddle stirrer. The stirrer was turnedat 350 rpm while 25 ml of concentrated (16M) nitric acid was addedrapidly. The dispersion gradually thickened to a gel. Stirring wasstopped for 15 minutes. When stirring was resumed at 350 rpm, 86 ml of1,1,2-trichloro-1,2,2-trifluoroethane was poured into the flask at arate of 300 ml/min. The gel immediately separated into copolymer andwater phases. Stirring was continued for 15 minutes, after which thetemperature was raised at a rate of 2.5° C./min to 45° C. by circulatinghot water through the jacket of the flask. A nitrogen purge was begun inthe flask to aid in solvent removal. Stirring at 45° C. was continuedfor 1 hour to remove the bulk of the solvent, and then the temperaturewas raised to 75° C. at a rate of 2.5° C./minute. A dip tube with filtercloth at the bottom was placed into the flask, and water was pumped outof the flask with a peristaltic pump at the rate of 45 ml/minute. Freshwater was added to the flask at the same rate in order to keep thevolume approximately constant. This washing was continued for about 2hours, or until the pH of the effluent water was 7 as determined with anindicator paper. At this point, water addition was stopped and all butabout 50 ml of water was removed from the flask.

Twenty-five ml of triethylamine was added to the flask, and the contentswere allowed to stir at 77° C. under reflux for 12 hours. The solidcopolymer was then recovered by vacuum filtration, washed twice with 100ml aliquots of demineralized water, then dried in a vacuum oven for 12hours at 100° C. The yield was 230 g of light brown polymer with a glasstransition temperature of 149° C., corresponding to a CTFE content of 35mole percent. The CTFE content was determined from a calibration curveof Tg vs. CTFE content, where CTFE content had been obtained by chlorineanalysis.

I claim:
 1. A metallic sheet or foil having on at least one face thereofa coating of an amorphous copolymer of 58-99 mole % ofperfluoro-2,2-dimethyl-1,3-dioxole with complementary amounts of morethan one comonomer selected from the class consisting of the followingcompounds:(a) tetrafluoroethylene, (b) chlorotrifluoroethylene, (c)vinylidene fluoride, (d) hexafluoropropylene, (e) trifluoroethylene, (f)perfluoro(alkyl vinyl ethers) of the formula CF2═CFORF, where RF is anormal perfluoroalkyl radical having 1-3 carbon atoms, (g) fluorovinylethers of the formula CF2═CFOQZ, where Q is a perfluorinated alkyleneradical containing 0-4 ether oxygen atoms, wherein the sum of the C andO atoms in Q is 2 to 10; and Z is a group selected from the classconsisting of --COOR, --SO2F, --CN, --COF, and --OCH3, where R is a C₁-C₄ alkyl, (h) vinyl fluoride, and (i) (perfluoroalkyl)ethylene,RfCH═CH2, where Rf is a C₁ -C₈ normal perfluoroalkyl radical; the glasstransition temperature of the copolymer being at least 140° C.; themaximum mole percentage, Ma . . . Mi, of each comonomer in thecopolymers being as follows: (a) for tetrafluoroethylene, Ma=35, (b) forchlorotrifluoroethylene, Mb=42, (c) for vinylidene fluoride, Mc=20, (d)for hexafluoropropylene, Md=15 (e) for trifluoroethylene, Me=30 (f) forCf2═CFORF, MF=30, (g) for CF2═CFOQZ, Mg=20, (h) for vinyl fluoride,Mh=25, and (i) for RfCH═CH2, Mi=10; and the amount of each comonomerother than perfluorodimethyl-1,3-dioxole being such that the sum, S, ofthe ratios of their mole percentages, ma . . . mi, to the maximumpercentage of all such comonomers taken together, 42 mole %, is nolarger than 1, as shown below:

    S=ma/42+mb/42+ . . . +mi/42≦1.


2. A metallic sheet or foil having on at least one face thereof acoating of an amorphous dipolymer of 58-99 mole % ofperfluoro-2,2-dimethyl-1,3-dioxole with a complementary amount of acomonomer selected from the class consisting of the followingcompounds:(a) chlorotrifluoroethylene, (b) vinylidene fluoride, (c)trifluoroethylene, (d) perfluoro(alkyl vinyl ethers) of the formulaCF2═CFORF, where RF is a normal perfluoroalkyl radical having 1-3 carbonatoms, (d) fluorovinyl ethers of the formula CF2═CFOQZ, where Q is aperfluorinated alkylene radical containing 0-4 ether oxygen atoms,wherein the sum of the C and O atoms in Q is 2 to 10; and Z is a groupselected from the class consisting of --COOR, --SO2F, --CN, --COF, and--OCH3, where R is a C1-C4 alkyl, (f) vinyl fluoride, and (g)(perfluoroalkyl)ethylene, RfCH═CH2, where Rf is a C1-C8 normalperfluoroalkyl radical, the glass transition temperature of thecopolymer being at least 140° C.; the maximum mole percentage, Mb . . .Mi, of the comonomer in the dipolymers being as follows: (a) forchlorotrifluoroethylene, Mb=42, (b) for vinylidene fluoride, Mc=20, (c)for trifluoroethylene, Me=30 (d) for CF2═CFORF, Mf=30, (e) forCR2═CFOQZ, Fg=20, (f) for vinyl fluoride, Mh=25, and (g) for RfCH═CH2,Mi=10.